to answer ur question its the back allen bolt on the body then u have to be care not to pinch the wire and the half the hop up unit slides out attached to the barrel. search the forums for more info put " tight bore barrel upgrade"

Just to answer your question if you do decide to do it your self when your warranty runs out.

1. Basically just slide your upper hop up unit out.
2. Once you have it out just give the barrel a good about 45 degree twist.
3. This is when you should see that small clamp that's puzzled in with the upper hop up coming off.
4. Pull that little clamp piece off.
5. Once it's off, just pull the inner barrel straight out. (Note the brass spacer, take it off and don't loose that)
6. Once you've got the inner barrel out the rubber sleeve at the back of the barrel is the hop up BUCKING. Slide that piece off.
7. Now your able to start installing the tightbore barrel.
8. Take your hop up BUCKING and slide it onto the back of new tightbore barrel, there is only one way to slide on the bucking so it shouldn't be hard at all. It's like a one piece puzzle, just match the grooves inside the bucking to the grooves at the back of the barrel.
9. Once you have the bucking on your new barrel slide the brass spacer on next.
10. Now just slide the inner barrel back into the upper hop up unit and hide that brass spacer under the tip of the hop up unit as it was before (Note, make sure that the two ditches at the back of your barrel are facing horizontally left and right outward, that's what keeps that little clamp locked into place so your barrel doesn't accidentally slips out, and that the open part at the back of the barrel faces upwards, that's where the little nub inside of the hop up unit itself presses down on the bb to grip it).
11. Now just snap that little black clamp back into place as it was before, and your new inner barrel is ready to rock.